1. C++ / Говнокод #27655

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    Если у меня есть приватный метод, то зачем мне его объявлять в .h-файле?
Хочу только в .cpp написать вспомогательный метод и только там его использовать.
А вынужден копипастить сигнатуру ещё и в .h.

    3_dar, 10 Сентября 2021

    Комментарии (151)

  2. C++ / Говнокод #27621

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    struct Foo {
};

struct Bar {
    int x[0];
};

    https://ideone.com/upuoOg

    Какая консистентность )))

    bormand, 27 Августа 2021

    Комментарии (88)

  3. C++ / Говнокод #27619

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    const int sum(int a, int b){
    return a+b;
}

int a(int x)
{
    const std::function<int(int)> sum4 = std::bind(sum,_1, 4);    
    return sum4(123);
}

int b(int x)
{
    puts("bagor");    
    const std::function<int(int)> sum4 = std::bind(sum,_1, 4);    
    return sum4(123);
}

int c(int x)
{
    const std::function<int(int)> sum4 = std::bind(sum,_1, 4);    
    puts("bagor");    
    return sum4(123);
}

// Функции a и b нормально инлайнятся. Ассемблерный выхлоп:

sum(int, int):                               # @sum(int, int)
        lea     eax, [rdi + rsi]
        ret
a(int):                                  # @a(int)
        mov     eax, 127
        ret
b(int):                                  # @b(int)
        push    rax
        mov     edi, offset .L.str
        call    puts
        mov     eax, 127
        pop     rcx
        ret

//А вот int c(int x)
c(int):                                  # @c(int)
        push    rbx
        sub     rsp, 32
        mov     edi, 16
        call    operator new(unsigned long)
        mov     rbx, rax
        mov     qword ptr [rax], offset sum(int, int)
        mov     dword ptr [rax + 8], 4
        mov     qword ptr [rsp], rax
        mov     qword ptr [rsp + 24], offset std::_Function_handler<int (int), std::_Bind<int const (*(std::_Placeholder<1>, int))(int, int)> >::_M_invoke(std::_Any_data const&, int&&)
        mov     qword ptr [rsp + 16], offset std::_Function_handler<int (int), std::_Bind<int const (*(std::_Placeholder<1>, int))(int, int)> >::_M_manager(std::_Any_data&, std::_Any_data const&, std::_Manager_operation)
        mov     edi, offset .L.str
        call    puts
        mov     esi, dword ptr [rbx + 8]
        mov     edi, 123
        call    qword ptr [rbx]
        mov     ebx, eax
        mov     rax, qword ptr [rsp + 16]
        test    rax, rax
        je      .LBB3_3
        mov     rdi, rsp
        mov     rsi, rdi
        mov     edx, 3
        call    rax
.LBB3_3:
        mov     eax, ebx
        add     rsp, 32
        pop     rbx
        ret
        mov     rdi, rax
        call    __clang_call_terminate
        mov     rbx, rax
        mov     rax, qword ptr [rsp + 16]
        test    rax, rax
        je      .LBB3_6
        mov     rdi, rsp
        mov     rsi, rdi
        mov     edx, 3
        call    rax
.LBB3_6:
        mov     rdi, rbx
        call    _Unwind_Resume@PLT
        mov     rdi, rax
        call    __clang_call_terminate
__clang_call_terminate:                 # @__clang_call_terminate
        push    rax
        call    __cxa_begin_catch
        call    std::terminate()
std::_Function_handler<int (int), std::_Bind<int const (*(std::_Placeholder<1>, int))(int, int)> >::_M_invoke(std::_Any_data const&, int&&): # @std::_Function_handler<int (int), std::_Bind<int const (*(std::_Placeholder<1>, int))(int, int)> >::_M_invoke(std::_Any_data const&, int&&)
        mov     rax, qword ptr [rdi]
        mov     rcx, qword ptr [rax]
        mov     edi, dword ptr [rsi]
        mov     esi, dword ptr [rax + 8]
        jmp     rcx                             # TAILCALL
std::_Function_handler<int (int), std::_Bind<int const (*(std::_Placeholder<1>, int))(int, int)> >::_M_manager(std::_Any_data&, std::_Any_data const&, std::_Manager_operation): # @std::_Function_handler<int (int), std::_Bind<int const (*(std::_Placeholder<1>, int))(int, int)> >::_M_manager(std::_Any_data&, std::_Any_data const&, std::_Manager_operation)

    Решил попробовать std::bind.

    https://godbolt.org/z/eW5eT5oj4

    3.14159265, 27 Августа 2021

    Комментарии (86)

  4. C++ / Говнокод #27614

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    struct file_id
{
    uint64_t        persistent;
    uint64_t        volatile_;

    static const size_t RAW_LENGTH  = 16;
    operator std::string() const
    { return std::string(reinterpret_cast<const char*>(&persistent), RAW_LENGTH); }

    // Операторы для использования file_id в качестве ключа map и 
    // unordered_map
    struct hash
    {
        std::size_t operator()(const ntdec_smb2_file_id& file_id) const
        {
            std::string s_file_id = file_id;
            std::hash<std::string> hasher;
            return hasher(s_file_id);
        }
    };

    bool operator == (const ntdec_smb2_file_id& other)
    {
        return std::string(*this) == std::string(other);
    }

    bool operator < (const ntdec_smb2_file_id& other)
    {
        return std::string(*this) < std::string(other);
    }

    bool operator > (const ntdec_smb2_file_id& other)
    {
        return std::string(*this) > std::string(other);
    }
};

    operator std::string тоже UB?

    YpaHeLI_, 24 Августа 2021

    Комментарии (11)

  5. C++ / Говнокод #27568

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    // https://github.com/seanbaxter/circle/blob/master/examples/README.md#tldr
// ...
// Circle's primary syntactic element is the @meta keyword, which runs the prefixed statement
// during source translation (or during template instantiation in dependent contexts).

// https://github.com/seanbaxter/circle/blob/master/examples/README.md#same-language-reflection
// duff1.cxx

void duff_copy1(char* dest, const char* source, size_t count) {
  const char* end = source + count;
  while(size_t count = end - source) {
    switch(count % 8) {
      case 0: *dest++ = *source++; // Fall-through to case 7
      case 7: *dest++ = *source++; // Fall-through to case 6...
      case 6: *dest++ = *source++;
      case 5: *dest++ = *source++;
      case 4: *dest++ = *source++;
      case 3: *dest++ = *source++;
      case 2: *dest++ = *source++;
      case 1: *dest++ = *source++;
      break;
    }
  }
}

// Reproduced above is a simplified version of Duff's device, an infamous memcpy function designed
// to reduce the amount of branching in the operation. (The loop is optimally interleaved with the switch,
// but I'm trying to illustrate some other points and don't want to add to the confusion.) Once we enter the
// switch, perform an assignment and unconditionally progress to the next case statement. This algorithm
// cries out for automation. The case statements have indices that run from 8 down to 1, modulo 8. Can we give it the Circle treatment?

// duff2.cxx

void duff_copy2(char* dest, const char* source, size_t count) {
  const char* end = source + count;
  while(size_t count = end - source) {
    switch(count % 8) {
      @meta for(int i = 8; i > 0; --i)
        case i % 8: *dest++ = *source++;
      break;
    }
  }

    Но гомоиконности таким подкостыливанием вы естественно не добавите!

    j123123, 14 Августа 2021

    Комментарии (21)

  6. C++ / Говнокод #27561

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    QSqlQuery& SQLConnect::get()
{
    if ( makeConnection() ) {
        query = QSqlQuery(mDb);
        return query;
    }
    QSqlQuery empty;
    return empty;
}

bool SQLConnect::makeConnection()
{
   mDb = SQLConnectPool::Instance().get();
   return true;
}

    Раньше компилилось и не замечал, а тут на новом компиляторе начал кидать ошибки и решил посмотреть, что же там напроектировали

    avk17, 14 Августа 2021

    Комментарии (12)

  7. C++ / Говнокод #27536

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    class Solution {
public:
    std::vector<std::vector<int>> diagonalSort(std::vector<std::vector<int>> & mat) {
        if (!mat.size()) return mat;
        
        const size_t rl = mat[0].size();
        const size_t cl = mat.size();
        
        sort(mat, rl, cl, 0, 0);
        for (size_t i = 1; i < rl; ++i) {
            sort(mat, rl, cl, 0, i);
        }
        for (size_t i = 1; i < cl; ++i) {
            sort(mat, rl, cl, i, 0);
        }
        
        return mat;
    }
private:
    void sort(std::vector<std::vector<int>> & mat, size_t rl, size_t cl, size_t i, size_t j) {
        const size_t len = std::min(rl - j, cl - i);
        const size_t endj = j + len;
        const size_t endi = i + len;
        std::sort(diag_iter<false>{&mat, i, j}, diag_iter<false>{&mat, endi, endj});
    }
    
    template <bool isConst>
    class diag_iter {
        std::vector<std::vector<int>> *base;
        size_t i, j;
        using T = int;
    public:
        using iterator_category = std::forward_iterator_tag;
        using difference_type   = std::ptrdiff_t;
        using value_type        = T;
        using pointer           = T*;
        using reference         = typename std::conditional<isConst, const T&, T&>::type;
        diag_iter(std::vector<std::vector<int>> *base, size_t i, size_t j) : base(base), i(i), j(j) { }
        diag_iter(const diag_iter&) = default;
        diag_iter& operator=(const diag_iter&) = default;
        ~diag_iter() = default;
        reference operator*() const { return (*base)[i][j]; }
        diag_iter& operator++() { i++; j++; return *this; }
        friend bool operator== (const diag_iter& a, const diag_iter& b) { return a.i == b.i && a.j == b.j; };
        friend bool operator!= (const diag_iter& a, const diag_iter& b) { return !(a == b); };
        pointer operator->() const { return &(this->operator*()); }
        diag_iter operator++(int) { diag_iter tmp = *this; ++(*this); return tmp; }
        diag_iter() = default;
        diag_iter& operator--() { i--; j--; return *this; }
        diag_iter operator--(int) { diag_iter tmp = *this; --(*this); return tmp; }
        diag_iter& operator+=(difference_type n) { i += n; j += n; return *this; }
        friend diag_iter operator+(diag_iter it, difference_type n) { return it += n; }
        diag_iter& operator-=(difference_type n) { i -= n; j -= n; return *this; }
        diag_iter operator-(difference_type n) const { return diag_iter(*this) -= n; }
        friend difference_type operator-(const diag_iter& a, const diag_iter& b) { return (b.j * b.base->size() + b.i) - (a.j * a.base->size() + a.i); }
        reference operator[](difference_type n) const { return *(*this + n); }
        friend bool operator<(const diag_iter& a, const diag_iter& b) { return b - a > 0; }
        friend bool operator>(const diag_iter& a, const diag_iter& b) { return b < a; }
        friend bool operator>=(const diag_iter& a, const diag_iter& b) { return !(a < b); }
        friend bool operator<=(const diag_iter& a, const diag_iter& b) { return !(a > b); }
    };
};

    https://leetcode.com/problems/sort-the-matrix-diagonally/

    Сортировка через итераторы оказалась примерно в три раза медленнее, чем через копирование в вектор, сортировку его и копирование обратно.

    grillow1337, 25 Июля 2021

    Комментарии (18)

  8. C++ / Говнокод #27533

    +1

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    #include <iostream>
#include <functional>

#define STD_FUNCTION(a, ...) typeof( a (*) __VA_ARGS__ )

template<typename T>
T do_op_t(T a, T b, STD_FUNCTION(T,(T,T)) op)
{
  return op(a,b);
}

template
<

  typename T,

  STD_FUNCTION(
    T,
    (
      T,T,
      STD_FUNCTION(
        T,
        (T,T)
      )
    )
  ) F1,

  STD_FUNCTION(
    T,
    (T,T)
  ) F2

>
T do_op_spec(T a, T b)
{
  return F1(a, b, F2);
}

int add(int a, int b) { return a + b; }

int mul(int a, int b) { return a * b; }

std::function<int(int,int)> fnc = \
  do_op_spec\
  <
    int,
    do_op_t<int>,
    add
  >;

int main()
{
  std::cout << do_op_t<int>(9, 9, add) << "\n";
  std::cout << do_op_t<int>(9, 9, mul) << "\n";
  std::cout << do_op_spec<int, do_op_t<int>,add>(9,9)  << "\n";
  std::cout << do_op_spec<int, do_op_t<int>,mul>(9,9)  << "\n";
  std::cout << fnc(9,9) << "\n";
}

    Какая крестопараша )))

    j123123, 23 Июля 2021

    Комментарии (95)

  9. C++ / Говнокод #27486

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    // https://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/global/qglobal.h?h=v5.13.1#n1017

#if __cplusplus >= 201703L
// Use C++17 if statement with initializer. User's code ends up in a else so
// scoping of different ifs is not broken
#define Q_FOREACH(variable, container)                                   \
for (auto _container_ = QtPrivate::qMakeForeachContainer(container);     \
     _container_.i != _container_.e;  ++_container_.i)                   \
    if (variable = *_container_.i; false) {} else
#else
// Explanation of the control word:
//  - it's initialized to 1
//  - that means both the inner and outer loops start
//  - if there were no breaks, at the end of the inner loop, it's set to 0, which
//    causes it to exit (the inner loop is run exactly once)
//  - at the end of the outer loop, it's inverted, so it becomes 1 again, allowing
//    the outer loop to continue executing
//  - if there was a break inside the inner loop, it will exit with control still
//    set to 1; in that case, the outer loop will invert it to 0 and will exit too
#define Q_FOREACH(variable, container)                                \
for (auto _container_ = QtPrivate::qMakeForeachContainer(container); \
     _container_.control && _container_.i != _container_.e;         \
     ++_container_.i, _container_.control ^= 1)                     \
    for (variable = *_container_.i; _container_.control; _container_.control = 0)
#endif

    А можно ли свой foreach сделать через какую-нибудь шаблонопарашу? Или тут, как обычно, нужна гомоиконность?

    j123123, 28 Июня 2021

    Комментарии (74)

  10. C++ / Говнокод #27483

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    #include <unistd.h>
#include <stdio.h>
#include <limits.h>

template<size_t Size> struct static_string {char data[Size];};
template<size_t ... Indexes>struct index_sequence {};
template<size_t Size, size_t ... Indexes>
constexpr static_string<sizeof ... (Indexes) + 1> make_static_string(const static_string<Size>& str,index_sequence<Indexes ...>) {return {str.data[Indexes] ..., '\0'};}
constexpr static_string<1> make_static_string() {return {'\0'};}
template<size_t Size, size_t ... Indexes>
struct make_index_sequence : make_index_sequence<Size - 1, Size - 1, Indexes ...> {};
template<size_t Size>
constexpr static_string<Size> make_static_string(const char (& str)[Size]) {return make_static_string(str, make_index_sequence<Size - 1>{});}
template<size_t ... Indexes>
struct make_index_sequence<0, Indexes ...> : index_sequence<Indexes ...> {};
template<size_t Size, size_t ... Indexes>
constexpr static_string<sizeof ... (Indexes) + 1> make_static_string(const char (& str)[Size],index_sequence<Indexes ...>) {return {str[Indexes] ..., '\0'};}
template<size_t Size>
constexpr size_t static_string_find(const static_string<Size>& str, char ch, size_t from, size_t nth) {return Size < 2 || from >= Size - 1 ? UINT_MAX :str.data[from] != ch ? static_string_find(str, ch, from + 1, nth) :nth > 0 ? static_string_find(str, ch, from + 1, nth - 1) : from;}
template<size_t Size>
constexpr size_t static_string_find_0(const static_string<Size>& str, char ch, size_t from, size_t nth) {return Size < 2 || from >= Size - 1 ? 0 : str.data[from] != ch ? static_string_find_0(str, ch, from + 1, nth) :nth > 0 ? static_string_find(str, ch, from + 1, nth - 1) : from;}
template<size_t Size1, size_t ... Indexes1, size_t Size2, size_t ... Indexes2>
constexpr static_string<Size1 + Size2 - 1> static_string_concat_2(const static_string<Size1>& str1, index_sequence<Indexes1 ...>,const static_string<Size2>& str2, index_sequence<Indexes2 ...>) {return {str1.data[Indexes1] ..., str2.data[Indexes2] ..., '\0'};}
template<size_t Size1, size_t Size2>
constexpr static_string<Size1 + Size2 - 1> static_string_concat_2(const static_string<Size1>& str1, const static_string<Size2>& str2) {return static_string_concat_2(str1, make_index_sequence<Size1 - 1>{},str2, make_index_sequence<Size2 - 1>{});}
template<size_t Begin, size_t End, size_t ... Indexes>
struct make_index_subsequence : make_index_subsequence<Begin, End - 1, End - 1, Indexes ...> {};
template<size_t Pos, size_t ... Indexes>
struct make_index_subsequence<Pos, Pos, Indexes ...> : index_sequence<Indexes ...> {};
template<size_t Begin, size_t End, size_t Size>
constexpr static_string<End - Begin + 1> static_string_substring(const static_string<Size>& str) {return make_static_string(str, make_index_subsequence<Begin, End>{});}
template<size_t Begin, size_t Size>
constexpr static_string<Size - Begin> static_string_suffix(const static_string<Size>& str) {return static_string_substring<Begin, Size - 1>(str);}
#define remove_underscore(arg) ([] () __attribute__((always_inline)) {constexpr auto a = static_string_find(make_static_string(arg),'_',0,0) == UINT_MAX? make_static_string(arg):static_string_concat_2(static_string_concat_2(static_string_substring<0,static_string_find_0(make_static_string(arg),'_',0,0)>(make_static_string(arg)),static_string_suffix<static_string_find_0(make_static_string(arg),'_',0,0)+1>(make_static_string(arg))),make_static_string("\0"));return a;}().data)

int main()
{
    puts(remove_underscore("_testtest"));
    puts(remove_underscore("test_test"));
    puts(remove_underscore("testtest_"));
}

    Убогий constexpr в c++11

    mittorn, 25 Июня 2021

    Комментарии (46)